Currently there are numerous consumer electronics communications devices such as portable multimedia players, add-ons for portable multimedia players, cellular telephones, personal digital assistants (PDAs), etc. that have the ability to playback audio on FM stereo radios. To accomplish this, these communication devices incorporate an FM transmitter for transmitting an FM signal typically at very low power levels to an FM radio located relatively close by. In a typical application, a communication devices is used to playback audio (i.e. music, etc.) through a car's built-in FM receiver. The FM transmitter functions to modulate the audio signal onto an FM carrier signal and broadcast the FM modulated audio signal. The FM carrier is set to a particular carrier frequency typically selected from a group of several available frequencies.
The FM radio receiver in the car must be manually tuned by a user to this frequency in order for the audio to be heard over the car's sound system. Since FM radio receivers do not have a mechanism of automatically tuning to the transmission frequency of the FM tuner, the FM radio must be tuned to the desired frequency manually.
Not only does the user have to manually tune the FM receiver to one of the frequencies available on the FM transmitter, but the selected frequency must not be occupied by a FM radio station. Either the selected frequency must not be occupied or the signal received from the FM radio station must be very weak that the signal generated by the FM transmitter is strong enough to overpower it. Further, in order to playback the audio over the car stereo system, the user must first find a quiet station that is one of the stations that the FM transmitter is capable of transmitting on. Both the transmitting frequency on the FM transmitter and the frequency the FM receiver is tuned to must be set manually by trial and error. By trial and error, the user eventually finds a station that is quiet enough to receive and playback the signal from the FM transmitter. Once tuned to that station, the user then manually configures the FM transmitter to transmit over that frequency.
It is therefore desirable to have a mechanism whereby a radio link between an FM transmitter incorporated in a communication device and an FM receiver is established automatically without the need for the user to manually tune the FM receiver to the desired frequency. It is also desirable that the mechanism also include automatic means of finding a quiet frequency over which to transmit the audio signal. The automatic setup of the connection should be accomplished with minimal latency. Ideally it is low enough to support phone conversations to enable the conveyance of audio signals from a cellular handset to the car radio thus creating a “car-kit” set.